Spray nozzles for high pressure cleaning applications direct a high velocity liquid stream against a surface to be cleaned. The liquid stream forcefully impinges against the surface in order to remove dirt or other particles thereon. Such nozzles, for example, are commonly used in pressure washers, car washes, and other cleaning applications. The trend has been to use increasingly higher liquid pressures in order to achieve greater impact forces. However, as the liquid pressure increases, increased turbulence within the spray nozzle and the discharging flow stream can disrupt and break up the concentration of the flow stream, thereby reducing its impact force. The resulting non-uniformity of the broken up stream further can result in inadequate and/or uneven cleaning of a surface. Heretofore it has been difficult to direct a concentrated solid liquid stream at relatively high liquid pressures.